The present invention concerns new filtration adjuvants, usable in the filtration of liquids, particularly beer at the end of the secondary fermentation storage. It also concerns a new filtration method using said new filtration adjuvants. It finally concerns a new method of regeneration in situ of said filtration adjuvants and new filtration supports.
Filtration adjuvants are substances used in solid-liquid separation in which a deposit is formed on a filter screen or a filter support, either alone or mixed with the substances to be retained, and procure efficient separation by primarily mechanical means.
The various types of filtration adjuvant can be distinguished by their main ingredients.
The type of filtration adjuvant most frequently used in brewing is kieselguhr, comprising mainly calcined diatoms.
Other types of filtration adjuvants include perlite obtained from volcanic rock, starch, cellulose and fibrous polymer synthetic materials.
During filtration, these various filtration adjuvants form a porous medium trapping the impurities to be eliminated and facilitating the flow of the liquid phase.
The filtration adjuvants described above can be used either in the so-called pre-layer technique or in the so-called "alluvion" technique.
One industrial sector in which filtration adjuvants are used is brewing.
Most commercially produced beers must have a bright color and be free of micro-organisms. These requirements are generally complied with when the beer has an E.B.C. (European Brewing Convention) clarity value less than 0.5.degree. EBC and a micro-organism content less than five yeasts per liter.
The E.B.C. clarity values and their assessment are defined in the publication: Analytica-E.B.C., 4th Ed., 1987, Revue de la Brasserie et des Boissons Ed., Zurich.
Until now the most economic and efficient method of obtaining these values has been to use a filtration adjuvant in making the beer.
After it has matured in secondary fermentation storage tanks, the beer must be clarified and filtered before it is packaged in order to eliminate a number of impurities, including colloidal material that makes it cloudy and yeast. After filtration the beer has a bright color and sufficient stability for an adequate shelf life.
Beer is usually filtered using filtration adjuvants and one of the following two techniques, namely "mass" filtration or "alluvion" filtration, the latter requiring a preliminary layer to be formed beforehand.
"Alluvion" filtration, by far and away the more commonly used technique, consists in depositing onto the filter medium, prior to filtration proper, a first preliminary layer of coarse filtration adjuvant to protect the filtration support (for example multiple tube filters or plate filters) and to facilitate demounting of the filter after filtration and cleaning of the filtration support. A second preliminary layer of filtration adjuvant similar in size to that used for "alluvion" filtering is frequently deposited in order to obtain a clear filtrate as soon as the filtration cycle starts.
In "alluvion" filtration, the filtration adjuvant is mixed with the beer before it is filtered and forms a suspension. During filtration this suspension forms a mixed cake containing impurities and the filtration adjuvant.
When the filtration cycle is finished, the filtration adjuvant cake containing the trapped impurities, in particular the yeasts, is eliminated in the form of a thick suspension generally referred to as slurry ("bourbe").
When multiple tube filters are used to carry out the filtration, a counterflow of a pressurized gas-water emulsion through the filter medium detaches the cake from the filter medium. It drops to the bottom of the filtration tank, where it is recovered.
If horizontal plate filters are used to carry out the filtration, the cake is eliminated by the centrifugal force produced by rotating the filter plates.
In "mass" filtration, the filtration adjuvant is deposited directly onto the filter support before the beer is filtered.
Using filtration adjuvants, especially kieselguhr, has a number of drawbacks, however.
One of the main drawbacks is that the filtration adjuvant can be used for only one filtration cycle.
The brewer is then obliged to discard the filtration adjuvant, in particular the kieselguhr, and to use a new amount of fresh filtration adjuvant. The environmental problems associated with this waste are readily apparent, quite apart from the additional cost of the end product related to the regular supply of fresh filtration adjuvants.
Techniques have therefore been considered for regenerating the filtration adjuvant, in particular kieselguhr, but they have not met all the requirements of the industry.
Current techniques for regenerating filtration adjuvants, in particular kieselguhr, succeed in only partial regeneration. The brewer is therefore obliged to add a certain amount of fresh filtration adjuvant on each new filtration cycle, to compensate for the loss in filtration efficiency due in particular to the increased quantity of impurities present, or even to discard the partially regenerated filtration adjuvant after several filtration cycles, with the problems already mentioned.
What is more, these processes require the use of special-purpose installations separate from the filtration installations. They therefore give rise to major investment and operating costs, in particular the cost of transporting the filtration adjuvant to the regeneration site.
Research has been carried out with the aim of developing a filtration adjuvant that can be regenerated and that solves the problems described above. One proposed filtration adjuvant of this type consists of spherical balls of synthetic material that can be regenerated in existing filtration installations. However, this filtration adjuvant is only a partial solution to the drawbacks mentioned above.
The substantially spherical shape of the filtration adjuvant particles necessitates the use of relatively large (&gt;100 .mu.m) particles to obtain acceptable permeability of the cake, and this leads to a thicker filter medium. Moreover, the filtration efficiency is generally insufficient.
What is more, the degree of regeneration achieved by the conventional techniques still proves unsatisfactory.